Marl pennant females are, at first glance, very similar to the spot-winged glider, which may be found in the same areas.   In fact, I mistakenly identified some of these as a spot-winged glider (the main difference is the black tip on the abdomen of the marl pennant).   Males have the same wing spots, but dark bodies.   The photos were taken along a dirt road at the west end of the Salton Sea, and along the Colorado River near Blythe, both in extreme southern California.   It was quite hot and these animals are in the 'obelisk' posture, pointing the abdomen at the sun to minimize heat gain.